Electrical testing system



Oct. 27, 1925. 8,5

H.|QYQL"$T ELECTRICAL TESTING SYSTEM- Filed July 1e, 1921 INVENTOR ATTORNEY Patented Oct. 27, 1925.

UNITED STATES PATENT OFFICE...

HARRY NYQUIST, OF IBLMHURST, NEW'YORK, ASSIGNOR- TO AMERICAN TELEPHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK.

nLEo'raicAI. rnsrme SYSTEM.

Application filed July 16, 1921.

To all whom it may concern:

Be it known that I, HARRY NYQUIST, re-- siding at Elmhurst, in the county of Queens and State'of New York, have invented certain Improvements in Electrical Testing Systems, of which the following is a specification.

This invention relates to electrical testing systems and particularly to an arrangement for determining the degree of unbalance between two networks, such as a signal transmission line and a network designed to bal ance the said line. I

In the copending application of Cory, Serial No. 485,207, filed July 16, 1521, there was disclosed a simple arrangement for detecting the presence of unbalance between a signaling circuit and an artificial line or balancing network intended to balance the signaling circuit. It is the'object of the present invention to provide an arrangement which not only indicates the existence of unbalance but also determines its magnitude.

This invention will be better understood from the following description when read in co-nection with the attached drawing,

which shows the terminal apparatus of a metallic duplex telegraph circuit which is arranged for the measurement of the unbalance that eXists between the line balancing network N and the line L.

In the figure, L represents a duplex telegraph signaling circuit having associated therewith a linev balancing network N I nterposed between the said line and its network is a relay R having line windings 1, 2, 3 and 4 connected in series therewith, and windings 5 and 6 connected in what is known as thevibratory circuit. All of the windings set forth above are wound upon the same magnetic core, the magnetic changes of which are intended to control the action of the armature 7. Bridged across the junction points of the windings 1-2 and winding-s 3& is the transmitter circuit 8, which has associated therewith. a

transmitter T and a transmitting branch filter F the function of which is to round off the signaling impulses created by the transmitter T When it is desired to measure unbalance between the line and its network, the circuit of relay It, is either disconnected at the points marked X, or the batteries 13 and 14: are disconnected so as Serial- N'o. 485,309.

to have no effect on the vibratory circuit. Bridged across the vibratory circuit which includes the windings 5 and 6 are the conductors 25 which are connected with the inner contacts of the switch 26. The swinging contacts of this switch are connected with the receiver 27 and a high frequency interrupter 28. Connected with the outer contacts of the switch 26 is a network 29 having a variable resistance bridged across its two sides and also having associated therewith a source of D. O. voltage 30 and a source of low frequency A. C. voltage 31, which may be of about cycles frequency.

The function of the network 29 and its associated sources of potential is to produce an electromotive force of variable magnitudeand wave shape such as to approxishown in the network may be so adjusted that the relative magnitudes of the two components of electromotive force may have any desired values. 1

The circuit connected with the distant end of the line L, would in general be the w same as shown in the figure except that the receiving circuit would not be opened as at X, and there would be no measuring circuit connected across the vibratory circuit as represented by the conductors in the Having in mind the foregoing description of the circuit shown in the figure the inven tion will be clearly understood from the following description of the mode of operation of the circuit.

Let it be assumed that telegraph signals, such as a series of reversals, are set up by the transmitter T and impressed by the output circuit 8 across the junction points of the windings 1-2 and 3- respectively. The current from the source will divide, part of it flowing through the windings 1 and 4: and the line L and the other part will flow through the windings 2 and 3 and the line balancing network N If the impedance of the balancing network at a definite frequency exactly equals that of the line L at the same frequency, the currents in the two paths W l be equal and no resultant receiver 27. and the interrupter 28. The

function of the interrupter is to break up the low frequency currents which have'been "induced in the windings?) and 6-by the operation .of the transmitter T thereby renderingaudible these low :frequency currents.

Iii-the switch 26 is operated so-astozinove the swinging. members to their outer contacts, the circuit containing"- the 1 receiver :27 and the interrupter 28 will be-connected'with the network 29 comprising "the source of comparative electromotive force. By adjusting the variable resistance element 32 associated with-the source 29. while operating the switch 26 at a uniforn1=1ate,-a:point'of adjustment of the resistance 32 will be reached where the tone producedby the receiver 27 will be the same whether connected with the-conductors 25 or with the source of comparative electromotive *lorce 29. The readingofthe adjustable element 82 indicates the extent-of the unbalance isting between the net-work N and the line L. The networkshould thenbeadjusted-so as to tend more nearly to balance the line L, and the testrpreviously described should be repeated, :By a seriesxoi tests and adjustments of the balancing network, the-unbalancegbetween a lineacircuit and its corresponding snetworkimay be :reduced ttoas low :a value as can 1 be obtained through the use of thedistortion bridge arrangementxlescribed in the .patent to N' y-quist- 1,435,328, dated November 14 1922.. The source of comparative electro-moti-ve force which is represented in the drawing by the network 29, including-the battery 30' and the :source of alternating currents 31 may be replaced by an equivalent source comprising a polechanger having asuitalble network-associated therewith to produce a suitable wave shape, such as, for example, :a condenser connected in seriesuvith the ,pole-changer. This pole-changer might be COIIHGCiEBCl'lIl a manner so as to be 'operazted. by the signal that is used in efi'ectingthe balanceand-thus better simulation of quality 'might be obtained. 1

Although this invention :has been disclosed in connection with tit dupleremetallic telegraph circuit, it is to be understood that it is'not limited'to such particular type of circuit but is capable of embodiment in other and different forms of-circuits without departing from the spirit and scope lot the appended claims,

KVhat isclaimed is:

1. I11 an electrical testing system, the combination with a line circuit, of a balancing network, "a "signal transmitting circuit,

a signal "receiving circuitQ-lroth etl'ectively 7 connected with the said line circuit and said network, and means connected with the said receiving circuit to measure the magnitude of the unbalance between the said line circuit-and the saidnetworkresult- 7 ing from the transmission of telegraph sig- .nal impulses, the said -means including a source of potentialfoncoinparison with the potentlal set up in said recelvlng clrcult by said network, and means for varying "the magnitudeof thevpotential from said'soi-irce.

2. In anelectricaltesting system, the combination with .a line circuit of a balancing.

unbalance -.between-zthe "line circuit and the network, a transmittingicircuit, a receiving circuit inductively related with reach of the other of said circuits, means connected with the said receiving circuit for indicating the difference between the-current fiowing from the said transmittingcircuit ,throughfthe said line circuit and ,through'the saidbalancing network, and a source ofcom-parative current to measure the magnitude of the unbalance current.

3. In an electrical testing systennthe combination with alineacircuitof a networkdesigned to substantially .;balance the said 'line circuit, a transmitting circuit, a receiving circuit, the said ,receivingycircuit being so related-to the said .line circuit and the said 'etwork that the impression by the said transmitting circuit of a voltageacross the said fline' circuit/and the said network will produce a voltage in the said" receiving circuit it thesaidnetwork fails to balance the said line circuit, a variablesource or comparative potential, and a current-indicating device adapted for alternate connection with the said source of comparative potential and .the said receiving circuit 'to indicatebalanee between thepotential of said source and -the unbalance vpotential of said receivingcircuit.

4. In antelectrical testing system, the

combination with a transmitting circuit, of

a plurality of networks in parallel therewith, a receiving-circuit inductively related to :the other of said circuits, and neutral with respect to transmitted signals if the said networks are balanced, and 'means connected with the said recelvlng circuit todetermine the magnitudeo f the unbalance curnetwork, a transmitting circuit and a reand across the source of comparative E. M. ceiving circuit characterized by freedom F. and adjusting the magnitude of the latirom transmitting interference when the said ter until the tone in the receiver is the same network balances its line circuit, the method when connected with the receiving circuit I of determining the magnitude of unbalance and withthe said source. 15 between the network and its line circuit, In testimony whereof, I have signed my which consists in impressing a signaling name to this specification this 15th day of wave across the said line circuit and its net July, 1921. work in parallel, connecting a detecting cir- 10 cuit alternately across the receiving circuit HARRY NYQUIST. 

